@google-cloud/bigtable 0.11.1 » Class: Filter

Filter

class

Constructor

Filter

new Filter()

A filter takes a row as input and produces an alternate view of the row based on specified rules. For example, a row filter might trim down a row to include just the cells from columns matching a given regular expression, or might return
all the cells of a row but not their values. More complicated filters can be composed out of these components to express requests such as, "within every column of a particular family, give just the two most recent cells which are
older than timestamp X."

There are two broad categories of filters (true filters and transformers), as well as two ways to compose simple filters into more complex ones (
Filter#interleave). They work as follows:

True filters alter the input row by excluding some of its cells wholesale from the output row. An example of a true filter is the
Filter#value filter, which excludes cells whose values don't match the specified pattern. All regex true filters use RE2 syntax (https://github.com/google/re2/wiki/Syntax) and are evaluated as full matches.
An important point to keep in mind is that RE2(.) is equivalent by default to RE2([^\n]), meaning that it does not match newlines. When attempting to match an arbitrary byte, you should therefore use the escape sequence '\C', which may
need to be further escaped as '\C' in your client language.

Transformers alter the input row by changing the values of some of its cells in the output, without excluding them completely. Currently, the only supported transformer is the Filter#valuestrip filter, which replaces every cell's value with the empty string.

The total serialized size of a filter message must not exceed 4096 bytes, and filters may not be nested within each other to a depth of more than 20.

Use the following table for the various examples found throughout the filter documentation.

column

column()

Matches only cells from columns whose qualifiers satisfy the given RE2 regex.

Note that, since column qualifiers can contain arbitrary bytes, the '\C' escape sequence must be used if a true wildcard is desired. The '.' character will not match the new line character '\n', which may be present in a binary qualifier.

Example

//-
// Using the following filter, we would retrieve the `tjefferson` and
// `gwashington` columns.
//-
var filter = [
{
column: /[a-z]+on$/
}
];
//-
// You can also provide a string (optionally containing regexp characters)
// for simple column filters.
//-
var filter = [
{
column: 'gwashington'
}
];
//-
// Or you can provide an array of strings if you wish to match against
// multiple columns.
//-
var filter = [
{
column: [
'gwashington',
'tjefferson'
]
}
];
//-
// If you wish to use additional column filters, consider using the following
// syntax.
//-
var filter = [
{
column: {
name: 'gwashington'
}
}
];
//-
// <h4>Column Cell Limits</h4>
//
// Matches only the most recent number of versions within each column. For
// example, if the `versions` is set to 2, this filter would only match
// columns updated at the two most recent timestamps.
//
// If duplicate cells are present, as is possible when using an
// {@link Filter#interleave} filter, each copy of the cell is
// counted separately.
//-
var filter = [
{
column: {
cellLimit: 2
}
}
];
//-
// <h4>Column Ranges</h4>
//
// Specifies a contiguous range of columns within a single column family.
// The range spans from <column_family>:<start_qualifier> to
// <column_family>:<end_qualifier>, where both bounds can be either
// inclusive or exclusive. By default both are inclusive.
//
// When the `start` bound is omitted it is interpreted as an empty string.
// When the `end` bound is omitted it is interpreted as Infinity.
//-
var filter = [
{
column: {
family: 'follows',
start: 'gwashington',
end: 'tjefferson'
}
}
];
//-
// By default, both the `start` and `end` bounds are inclusive. You can
// override these by providing an object explicity stating whether or not it
// is `inclusive`.
//-
var filter = [
{
column: {
family: 'follows',
start: {
value: 'gwashington',
inclusive: false
},
end: {
value: 'jadams',
inclusive: false
}
}
}
];

condition

condition()

A filter which evaluates one of two possible filters, depending on whether or not a test filter outputs any cells from the input row.

IMPORTANT NOTE: The test filter does not execute atomically with the pass and fail filters, which may lead to inconsistent or unexpected results. Additionally, condition filters have poor performance, especially when filters
are set for the fail condition.

Example

//-
// In the following example we're creating a filter that will check if
// `gwashington` follows `tjefferson`. If he does, we'll get all of the
// `gwashington` data. If he does not, we'll instead return all of the
// `tjefferson` data.
//-
var filter = [
{
condition: {
// If `test` outputs any cells, then `pass` will be evaluated on the
// input row. Otherwise `fail` will be evaluated.
test: [
{
row: 'gwashington'
},
{
family: 'follows'
},
{
column: 'tjefferson'
}
],
// If omitted, no results will be returned in the true case.
pass: [
{
row: 'gwashington'
}
],
// If omitted, no results will be returned in the false case.
fail: [
{
row: 'tjefferson'
}
]
}
}
];

family

family()

Matches only cells from columns whose families satisfy the given RE2 regex. For technical reasons, the regex must not contain the ':' character, even if it is not being used as a literal. Note that, since column families cannot contain the
new line character '\n', it is sufficient to use '.' as a full wildcard when matching column family names.

Example

var filter = [
{
family: 'follows'
}
];

interleave

interleave()

Applies several filters to the data in parallel and combines the results.

The elements of "filters" all process a copy of the input row, and the results are pooled, sorted, and combined into a single output row. If multiple cells are produced with the same column and timestamp, they will all appear in
the output row in an unspecified mutual order. All interleaved filters are executed atomically.

label

Applies the given label to all cells in the output row. This allows the client to determine which results were produced from which part of the filter.

Values must be at most 15 characters in length, and match the RE2 pattern [a-z0-9-]+

Due to a technical limitation, it is not currently possible to apply multiple labels to a cell. As a result, a chain filter may have no more than one sub-filter which contains a apply label transformer. It is okay for an Filter#interleave to contain multiple apply label transformers, as they will be applied to separate copies of the input. This may be relaxed in the future.

Example

var filter = {
label: 'my-label'
};

row

row()

Example

//-
// Matches only cells from rows whose keys satisfy the given RE2 regex. In
// other words, passes through the entire row when the key matches, and
// otherwise produces an empty row.
//
// Note that, since row keys can contain arbitrary bytes, the '\C' escape
// sequence must be used if a true wildcard is desired. The '.' character
// will not match the new line character '\n', which may be present in a
// binary key.
//
// In the following example we'll use a regular expression to match all
// row keys ending with the letters "on", which would then yield
// `gwashington` and `tjefferson`.
//-
var filter = [
{
row: /[a-z]+on$/
}
];
//-
// You can also provide a string (optionally containing regexp characters)
// for simple key filters.
//-
var filter = [
{
row: 'gwashington'
}
];
//-
// Or you can provide an array of strings if you wish to match against
// multiple keys.
//-
var filter = [
{
row: [
'gwashington',
'tjefferson'
]
}
];
//-
// If you wish to use additional row filters, consider using the following
// syntax.
//-
var filter = [
{
row: {
key: 'gwashington'
}
}
];
//-
// <h4>Row Samples</h4>
//
// Matches all cells from a row with probability p, and matches no cells
// from the row with probability 1-p.
//-
var filter = [
{
row: {
sample: 1
}
}
];
//-
// <h4>Row Cell Offsets</h4>
//
// Skips the first N cells of each row, matching all subsequent cells.
// If duplicate cells are present, as is possible when using an
// {@link Filter#interleave}, each copy of the cell is counted
// separately.
//-
var filter = [
{
row: {
cellOffset: 2
}
}
];
//-
// <h4>Row Cell Limits</h4>
//
// Matches only the first N cells of each row.
// If duplicate cells are present, as is possible when using an
// {@link Filter#interleave}, each copy of the cell is counted
// separately.
//-
var filter = [
{
row: {
cellLimit: 4
}
}
];

set

set(key, value)

Stores a filter object.

Parameter

key

string

Filter name.

value

any type

Filter value.

sink

sink()

This filter is meant for advanced use only. Hook for introspection into the filter. Outputs all cells directly to the output of the read rather than to any parent filter.

Despite being excluded by the qualifier filter, a copy of every cell that reaches the sink is present in the final result.

As with an Filter#interleave filter, duplicate cells are possible, and appear in an unspecified mutual order.

Example

//-
// Using the following filter, a copy of every cell that reaches the sink is
// present in the final result, despite being excluded by the qualifier
// filter
//-
var filter = [
{
family: 'follows'
},
{
interleave: [
[
{
all: true
}
],
[
{
label: 'prezzy'
},
{
sink: true
}
]
]
},
{
column: 'gwashington'
}
];
//-
// As with an {@link Filter#interleave} filter, duplicate cells
// are possible, and appear in an unspecified mutual order. In this case we
// have a duplicates with multiple `gwashington` columns because one copy
// passed through the {@link Filter#all} filter while the other was
// passed through the {@link Filter#label} and sink. Note that one
// copy has label "prezzy" while the other does not.
//-

time

Example

toProto

toProto()

If we detect multiple filters, we'll assume it's a chain filter and the execution of the filters will be the order in which they were specified.

value

value()

Matches only cells with values that satisfy the given regular expression. Note that, since cell values can contain arbitrary bytes, the '\C' escape sequence must be used if a true wildcard is desired. The '.' character will not match the
new line character '\n', which may be present in a binary value.